This preliminary prospectus supplement relates to an effective registration statement under
the Securities Act of 1933, as amended, but the information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell and are not
soliciting an offer to buy these securities in any jurisdiction where the offer and sale is not permitted.

Filed Pursuant to Rule 497 Registration Statement No. 333-202531

SUBJECT TO COMPLETION, DATED June 19, 2017

PRELIMINARY PROSPECTUS SUPPLEMENT

(To Prospectus dated April 18,
2017)

1,500,000 Shares

Common Stock

Fidus Investment Corporation is an externally managed, closed-end, non-diversified management investment company that has elected to be
regulated as a business development company, or BDC, under the Investment Company Act of 1940, as amended, or the 1940 Act. We are offering 1,500,000 shares of our common stock.

Our common stock is listed on the Nasdaq Global Select Market under the symbol FDUS. On June 16, 2017, the last reported
sale price of our common stock was $17.08 per share. We are required to determine the net asset value per share of our common stock on a quarterly basis. As of March 31, 2017, our net asset value was $15.80 per share.

We generally invest in securities that would be rated below investment grade if they were rated by rating agencies. Below investment
grade securities, which are often referred to as high yield or junk, have speculative characteristics with respect to the issuers capacity to pay interest and repay principal.

Investing in our common stock is speculative and involves numerous risks, including risks associated with leverage and dilution. For
more information regarding these risks, please see Risk Factors beginning on page 12 of the accompanying prospectus.

Please read this prospectus supplement and the accompanying prospectus before investing, and keep it for future reference. It concisely sets forth important information about us that a prospective
investor should know before investing in our securities. We file annual, quarterly and current reports, proxy statements and other information about us with the Securities and Exchange Commission. This information is available free of charge by
contacting us at 1603 Orrington Avenue, Suite 1005, Evanston, Illinois 60201, Attention: Investor Relations, by accessing our website at http://www.fdus.com or by calling us collect at (847) 859-3940. Information contained on our website is not
incorporated by reference into, and you should not consider that information to be part of, this prospectus supplement or the accompanying prospectus. The Securities and Exchange Commission also maintains a website at http://www.sec.gov that
contains such information.

The Securities and Exchange Commission has not approved or disapproved of these securities
or determined if this preliminary prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Per Share

Total

Public offering price

$

$

Underwriting discount payable by us ( %)

$

$

Proceeds, before expenses, to us (1)

$

$

(1)

We estimate that we will incur approximately $200,000 in offering expenses in connection with this offering.

The underwriters have the option to purchase up to an additional 225,000 shares of common stock at the public offering price, less the
underwriting discount, within 30 days from the date of this preliminary prospectus supplement. If the option is exercised in full, the total public offering price will be
$ , the total underwriting discount ( ) will be $ , and the total proceeds to us, before deducting
estimated expenses payable by us of $200,000, will be $ .

The underwriters expect to deliver the shares on or about June , 2017.

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of the common stock we
are offering and certain other matters relating to us. The second part, the accompanying prospectus, gives more general information about the securities that we may offer from time to time, some of which may not apply to the common stock offered by
this prospectus supplement. For information about our common stock, see Description of Our Capital Stock in the accompanying prospectus.

If information varies between this prospectus supplement and the accompanying prospectus, you should rely only on such information in this prospectus supplement. The information contained in this
prospectus supplement supersedes any inconsistent information included in the accompanying prospectus. In various places in this prospectus supplement and the accompanying prospectus, we refer you to other sections of such documents for additional
information by indicating the caption heading of such other sections. The page on which each principal caption included in this prospectus supplement and the accompanying prospectus can be found is listed in the table of contents above. All such
cross references in this prospectus supplement are to captions contained in this prospectus supplement and not in the accompanying prospectus, unless otherwise stated.

YOU SHOULD RELY ONLY ON THE INFORMATION CONTAINED IN THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS. WE HAVE NOT, AND THE UNDERWRITERS HAVE NOT, AUTHORIZED ANY OTHER PERSON TO PROVIDE YOU
WITH DIFFERENT OR ADDITIONAL INFORMATION. IF ANYONE PROVIDES YOU WITH DIFFERENT OR ADDITIONAL INFORMATION, YOU SHOULD NOT RELY ON IT. WE ARE NOT, AND THE UNDERWRITERS ARE NOT, MAKING AN OFFER TO SELL THESE SECURITIES IN ANY JURISDICTION WHERE THE
OFFER OR SALE IS NOT PERMITTED. YOU SHOULD ASSUME THAT THE INFORMATION APPEARING IN THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS IS ACCURATE ONLY AS OF THEIR RESPECTIVE DATES, REGARDLESS OF THE TIME OF DELIVERY OF THIS PROSPECTUS
SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS OR ANY SALES OF THE SECURITIES. OUR BUSINESS, FINANCIAL CONDITION, RESULTS OF OPERATIONS AND PROSPECTS MAY HAVE CHANGED SINCE THOSE DATES.

This summary highlights some of the information in this prospectus supplement. It is not complete and may not contain all of the
information that you may want to consider. You should read the entire prospectus supplement and the accompanying prospectus carefully, including Risk Factors, Capitalization, Selected Consolidated Financial Data,
Managements Discussion and Analysis of Financial Condition and Results of Operations and the financial statements contained elsewhere in this prospectus supplement and the accompanying prospectus. Together, these documents describe
the specific terms of the shares we are offering. Except as otherwise noted, all information in this prospectus supplement and the accompanying prospectus assumes no exercise of the underwriters option to purchase additional shares.

Fidus Investment Corporation is a Maryland corporation, formed on February 14, 2011, for the purpose of acquiring
100.0% of the equity interests in Fidus Mezzanine Capital, L.P., or Fund I, and its general partner, Fidus Mezzanine Capital GP, LLC, or FMCGP, raising capital in its initial public offering, or IPO, which was completed in June 2011, and thereafter,
operating as an externally managed BDC under the 1940 Act. Fund I is licensed as a small business investment company, or SBIC, by the United States Small Business Administration, or SBA. Simultaneously with the consummation of our IPO, we acquired
all of the equity interests in Fund I and its former general partner as described elsewhere in this prospectus supplement under Formation Transactions, whereby Fund I became our wholly-owned subsidiary. On March 29, 2013, we
commenced operations of a new wholly-owned investment fund, Fidus Mezzanine Capital II, L.P., or Fund II, and on May 28, 2013, were granted a second license by the SBA to operate Fund II as an SBIC. Collectively, Fund I and Fund II are referred
to as the Funds. Unless otherwise noted in this prospectus supplement the terms we, us, our, the Company, Fidus and FIC refer to Fidus Investment Corporation and its
consolidated subsidiaries.

As used in this prospectus supplement the term our investment advisor refers to
Fidus Capital, LLC prior to the Formation Transactions and Fidus Investment Advisors, LLC after the Formation Transactions. The investment professionals of Fidus Investment Advisors, LLC were also the investment professionals of Fidus Capital, LLC.

Fidus Investment Corporation

We provide customized debt and equity financing solutions to lower middle-market companies, which we define as U.S.-based companies having revenues between $10.0 million and $150.0 million. Our investment
objective is to provide attractive risk-adjusted returns by generating both current income from our debt investments and capital appreciation from our equity related investments. Our investment strategy includes partnering with business owners,
management teams and financial sponsors by providing customized financing for ownership transactions, recapitalizations, strategic acquisitions, business expansion and other growth initiatives. We seek to maintain a diversified portfolio of
investments in order to help mitigate the potential effects of adverse economic events related to particular companies, regions or industries.

We invest in companies that possess some or all of the following attributes: predictable revenues; positive cash flows; defensible and/or leading market positions; diversified customer and supplier bases;
and proven management teams with strong operating discipline. We target companies in the lower middle-market with annual earnings, before interest, taxes, depreciation and amortization, or EBITDA, between $3.0 million and $20.0 million; however, we
may from time

to time opportunistically make investments in larger or smaller companies. Our investments typically range between $5.0 million and $25.0 million per portfolio company.

As of March 31, 2017, the fair value of our investment portfolio totaled $536.6 million and consisted of 55 active portfolio
companies and four portfolio companies that have sold their underlying operations. The weighted average yield on debt investments as of March 31, 2017 was 12.9%. The weighted average yield of our debt investments is not the same as a return on
investment for our stockholders but, rather, relates to a portion of our investment portfolio and is calculated before the payment of all of our fees and expenses. The weighted average yield was computed using the effective interest rates for debt
investments at cost as of March 31, 2017, including the accretion of original issue discount and loan origination fees, but excluding investments on non-accrual status, if any. There can be no assurance that the weighted average yield will
remain at its current level.

Market Opportunity

We believe that the limited amount of capital available to lower middle-market companies, coupled with the desire of these companies for flexible and partnership-oriented sources of capital, creates an
attractive investment environment for us. From our perspective, lower middle-market companies have faced difficulty raising debt capital in both the capital markets and private markets. As a result of the difficulties in the credit markets and fewer
sources of capital for lower middle-market companies, we see opportunities for improved risk-adjusted returns. Furthermore, we believe with a large pool of uninvested private equity capital seeking debt capital to complete transactions and a
substantial supply of refinancing opportunities, there is an opportunity to attain appealing risk-adjusted returns on debt and equity investments. See The Company in the accompanying prospectus for more information.

Business Strategy

We
intend to accomplish our goal of becoming the premier provider of capital to and value-added partner of lower middle-market companies by:

We use the following criteria and
guidelines in evaluating investment opportunities and constructing our portfolio. However, not all of these criteria and guidelines have been, or will be, met in connection with each of our investments.

Value Orientation / Positive Cash Flow. Our investment advisor places a premium
on analysis of business fundamentals from an investors perspective and has a distinct value orientation. We focus on companies with proven business models in which we can invest at relatively low multiples of operating cash flow. We also
typically invest in portfolio companies with a history of profitability and minimum trailing twelve month EBITDA of $3.0 million. We do not invest in start-up companies, turn-around situations or companies that we believe have unproven
business plans.

Experienced Management Teams with Meaningful Equity Ownership. We target portfolio companies that have
management teams with significant experience and/or relevant industry experience coupled with meaningful equity ownership. We believe management teams with these attributes are more likely to manage the companies in a manner that protects our debt
investment and enhances the value of our equity investment.

Niche Market Leaders with Defensible Market Positions. We
seek to invest in portfolio companies that have developed defensible and/or leading positions within their respective markets or market niches and are well positioned to capitalize on growth opportunities. We favor companies that demonstrate
significant competitive advantages, which we believe helps to protect their market position and profitability.

Diversified
Customer and Supplier Base. We prefer to invest in portfolio companies that have a diversified customer and supplier base. Companies with a diversified customer and supplier base are generally better able to endure economic downturns, industry
consolidation and shifting customer preferences.

Significant Equity Value. We believe the existence of significant
underlying equity value provides important support to our debt investments. With respect to our debt investments, we look for portfolio companies where management/sponsors have provided significant equity funding and where we believe aggregate
enterprise value significantly exceeds aggregate indebtedness, after consideration of our investment.

Viable Exit
Strategy. We invest in portfolio companies that we believe will provide steady cash flows to service our debt, ultimately repay our loans and provide working capital for their respective businesses. In addition, we seek to invest in portfolio
companies whose business models and expected future cash flows offer attractive exit possibilities for our equity investments. We expect to exit our investments typically through one of three scenarios: (a) the sale of the portfolio company
resulting in repayment of all outstanding debt and monetization of equity; (b) the recapitalization of the portfolio company through which our investments are replaced with debt or equity from a third party or parties; or (c) the repayment
of the initial or remaining principal amount of our debt investment from cash flow generated by the portfolio company. In some investments, there may be scheduled amortization of some portion of our debt investment that would result in a partial
exit of our investment prior to the maturity of the debt investment.

About our Advisor

Our investment activities are managed by Fidus Investment Advisors, LLC, our investment advisor, and supervised by our board of
directors, a majority of whom are not interested persons of Fidus as defined in Section 2(a)(19) of the 1940 Act, and who we refer to hereafter as the Independent Directors. Pursuant to the terms of the investment advisory and
management agreement, which we refer to as the Investment Advisory Agreement, between us and our

investment advisor, our investment advisor is responsible for determining the composition of our portfolio, including sourcing potential investments, conducting research and diligence on
potential investments and equity sponsors, analyzing investment opportunities, structuring our investments and monitoring our investments and portfolio companies on an ongoing basis. Our investment advisors investment professionals seek to
capitalize on their significant deal origination and sourcing, underwriting, due diligence, investment structuring, execution, portfolio management and monitoring experience. These professionals have developed a broad network of contacts within the
investment community, have gained extensive experience investing in assets that constitute our primary focus and have expertise in investing across all levels of the capital structure of lower middle-market companies. For information regarding the
people who control our investment advisor and their affiliations with us, see Certain Relationships and Related TransactionsInvestment Advisory Agreement in the accompanying prospectus.

Our relationship with our investment advisor is governed by and dependent on the Investment Advisory Agreement and may be subject to
conflicts of interest. We pay our investment advisor a fee for its services under the Investment Advisory Agreement consisting of two components  a base management fee and an incentive fee. The base management fee is calculated at an annual
rate of 1.75% of the average value of our total assets (other than cash or cash equivalents but including assets purchased with borrowed amounts). The incentive fee consists of two parts. The first part is calculated and payable quarterly in arrears
and equals 20.0% of our pre-incentive fee net investment income for the immediately preceding quarter, subject to a 2.0% preferred return, or hurdle, and a catch up feature. The second part is determined and
payable in arrears as of the end of each fiscal year in an amount equal to 20.0% of our realized capital gains, if any, on a cumulative basis from inception through the end of each fiscal year, computed net of all realized capital losses and
unrealized capital depreciation on a cumulative basis, less the aggregate amount of any capital gain incentive fees paid in prior years. We accrue, but do not pay, a capital gains incentive fee in connection with any unrealized capital appreciation,
as appropriate. For more information about how we compensate our investment advisor and the related conflicts of interest, see Management and Other AgreementsInvestment Advisory Agreement and Certain Relationships and Related
TransactionsConflicts of Interest in the accompanying prospectus.

Among other things, our board of directors is
charged with protecting our interests by monitoring how our investment advisor addresses conflicts of interest associated with its management services and compensation. Our board of directors is not expected to review or approve each borrowing or
incurrence of leverage. However, our board of directors periodically reviews our investment advisors portfolio management decisions and portfolio performance. In addition, our board of directors at least annually reviews the services provided
by and fees paid to our investment advisor. In connection with these reviews, our board of directors, including a majority of our Independent Directors, considers whether the fees and expenses (including those related to leverage) that we pay to our
investment advisor are fair and reasonable in relation to the services provided. Renewal of our Investment Advisory Agreement must be approved each year by our board of directors, including a majority of our Independent Directors.

With respect to the administrative agreement with our investment advisor, which also serves as our administrator, our board of directors
reviews the methodology employed in determining how the expenses are allocated to us. Our board of directors assesses the reasonableness of such reimbursements for expenses allocated to us based on the breadth, depth and quality of such services as
compared to the estimated cost to us of obtaining similar services from third-party service providers known to be available. In addition, our board of directors considers whether any third-party service provider would be capable of providing all
such services at comparable cost and quality.

Fidus Investment Advisors, LLC is a Delaware limited liability company that is
registered as an investment advisor under the Investment Advisers Act of 1940, as amended, or the Advisers Act. In addition, Fidus Investment Advisors, LLC provides us with office space, equipment and clerical, book-keeping and record-keeping
services pursuant to an administration agreement, which we refer to as the Administration Agreement.

Operating and Regulatory Structure

Our investment activities are managed by our investment advisor and supervised by our board of directors, a majority of
whom are not interested persons of us, our investment advisor or its affiliates.

As a BDC, we are required to comply with
certain regulatory requirements. For example, while we are permitted to finance investments using leverage, which may include the issuance of shares of preferred stock, or notes and other borrowings, our ability to use leverage is limited in
significant respects. See Regulation in the accompanying prospectus. Any decision on our part to use leverage will depend upon our assessment of the attractiveness of available investment opportunities in relation to the costs and
perceived risks of such leverage. The use of leverage to finance investments creates certain risks and potential conflicts of interest. See Risk FactorsRisks Relating to Our Business and Structure  Regulations governing our
operations as a BDC affect our ability to raise, and the way in which we raise, additional capital which may have a negative effect on our growth and Risk Factors  Risks Relating to Our Business and StructureBecause we borrow
money and may in the future issue additional senior securities including preferred stock and debt securities, the potential for gain or loss on amounts invested in us is magnified and may increase the risk of investing in us in the
accompanying prospectus.

We have elected to be treated for U.S. federal income tax purposes as a regulated investment
company, or RIC, under Subchapter M of the Internal Revenue Code of 1986, as amended, or the Code. In order to maintain our tax treatment as a RIC, we must satisfy certain source of income, asset diversification and distribution requirements. See
Material U.S. Federal Income Tax Considerations in the accompanying prospectus.

Risk Factors

The value of our assets, as well as the market price of our shares, will fluctuate. Our investments may be risky, and you may lose part
of or all of your investment in us. Investing in our securities involves other risks, including the following:

the general economy and its impact on the industries in which we invest;



risks associated with investing in lower middle-market companies;



the ability of our investment advisor to identify, invest in and monitor companies that meet our investment criteria; and



our ability to invest in qualifying assets.

See Risk Factors beginning on page 12 of the accompanying prospectus for additional factors you should carefully consider before deciding to invest in our securities.

Recent Developments

On
April 7, 2017, we sold our equity investment in Anatrace Products, LLC for a realized gain of $0.9 million.

On
May 1, 2017, our board of directors declared a regular quarterly dividend of $0.39 per share payable on June 23, 2017 to our stockholders of record as of June 9, 2017.

On May 24, 2017, we invested $11.5 million in a subordinated term loan and common equity of NGT Acquisition Holdings, LLC, a market
leader in the fragmented cutting tools and tool holders market.

On June 9, 2017, we exited our debt investments in
inthinc Technology Solutions, Inc. We received payment in full of $6.8 million on our subordinated loans, including a prepayment penalty.

On June 15, 2017, our stockholders voted to allow us to sell or otherwise issue common stock at a price below net asset value per share for a period of one year ending on the earlier of June 15, 2018 or
the date of our 2018 Annual Meeting of Stockholders.

1,500,000 shares of our common stock. We have granted the underwriters the option to purchase up to an additional 225,000 shares on the same terms within 30 days of the date of this prospectus
supplement.

Common stock outstanding prior to this offering

22,457,576 shares

Common stock to be outstanding after this offering (1)

23,957,576 shares

Use of proceeds

The net proceeds from this offering (without exercise of the underwriters option and before deducting estimated offering expenses payable by us of approximately $200,000) will be
$ .

We intend to use the net proceeds from this offering to make investments in lower middle-market companies in accordance with our investment objective and strategies, to
repay the outstanding indebtedness under our senior secured revolving credit agreement with ING Capital LLC (ING) (the Credit Facility), to increase our borrowing capacity under the SBIC Debenture Program and for working
capital and general corporate purposes. See Use of Proceeds in this prospectus supplement for more information.

Dividends and Distributions

We pay quarterly distributions to our stockholders out of assets legally available for distribution. Our distributions, if any, will be determined by our board of directors. Our ability to
declare distributions depends on our earnings, our overall financial condition (including our liquidity position), qualification for or maintenance of our RIC status and such other factors as our board of directors may deem relevant from time to
time.

When we make distributions, we will be required to determine the extent to which such distributions are paid out of current or accumulated earnings, recognized capital
gains or capital. To the extent there is a return of capital, investors will be required to reduce their basis in our stock for U.S. federal income tax purposes. In the future, our distributions may include a return of capital.

Taxation

We have elected to be treated as a RIC for U.S. federal income tax purposes. Accordingly, we generally will not pay corporate-level U.S. federal income taxes on any net ordinary income or
capital gains that we distribute to our

stockholders. To maintain our tax treatment as a RIC and the associated tax benefits, we must meet specified source-of-income and asset diversification requirements and distribute annually at
least 90% of our realized net ordinary income and realized net short-term capital gains, if any, in excess of our net long-term capital losses. See Distributions and Material U.S. Federal Income Tax Considerations in the
accompanying prospectus.

Effective trading at a discount

Shares of closed-end investment companies, including BDCs, frequently trade at a discount to their net asset value. The risk that our shares may trade at a discount to our net asset value is
separate and distinct from the risk that our net asset value per share may decline. We cannot predict whether our shares will trade above, at or below net asset value. See Risk Factors and Sales of Common Stock Below Net Asset
Value in the accompanying prospectus.

Risk factors

See Risk Factors beginning on page 12 of the accompanying prospectus for a discussion of risks you should carefully consider before deciding to invest in shares of our common stock.

(1)

The number of shares of common stock to be outstanding after this offering excludes 225,000 shares of common stock that the underwriters have an option to purchase.

For additional information regarding our common stock, see Description of Our Capital Stock in the
accompanying prospectus.

The following table is intended to assist you in understanding the costs and expenses that an investor in our common stock will bear,
directly or indirectly, based on the assumptions set forth below. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus supplement
contains a reference to fees or expenses paid by you, us, the Company or Fidus, or that we will pay fees or expenses, stockholders will indirectly bear such fees or expenses as investors in
us.

Stockholder transaction expenses:

Sales load borne by us (as a percentage of offering price)

%(1)

Offering expenses borne by us (as a percentage of offering price)

%(2)

Dividend reinvestment plan expenses



(3)

Total stockholder transaction expenses paid by us (as a percentage of offering price)

%

Annual expenses (as a percentage of net assets attributable to common stock)(4):

Base management fee

2.61

%(5)

Incentive fees payable under Investment Advisory Agreement

2.31

%(6)

Interest payments on borrowed funds

2.33

%(7)

Other expenses

1.24

%(8)

Total annual expenses

8.49

%(9)

(1)

Represents the sales load to be paid by us with respect to the shares of common stock to be sold by us in this offering.

(2)

The offering expenses of this offering are estimated to be approximately $200,000. If the underwriters exercise their option to purchase additional shares in full, the
offering expenses (as a percentage of the offering price) will be XX%.

(3)

The expenses of administering our dividend reinvestment plan are included in other expenses.

(4)

Annual expenses is calculated as a percentage of net assets attributable to common stock because such expenses are ultimately paid by our common
stockholders. Offering expenses, if any, will be borne directly or indirectly by our common stockholders. Net assets attributable to common stock equals average net assets, which is calculated as the average of the net assets balances as of
March 31, 2017 and the prior year end.

(5)

Our base management fee is 1.75% of the average value of our total assets (other than cash and cash equivalents but including assets purchased with borrowed amounts)
and are estimated by assuming the base management fee remains consistent with the fees incurred for the three months ended March 31, 2017. We may from time to time decide it is appropriate to change the terms of the Investment Advisory
Agreement. Under the 1940 Act, any material change to our Investment Advisory Agreement must be submitted to our stockholders for approval. The 2.61% reflected in the table is calculated on our net assets (rather than our total assets). See
Management and Other AgreementsInvestment Advisory Agreement in the accompanying prospectus.

(6)

This item represents an estimate of our investment advisors incentive fees assuming the incentive fee related to pre-incentive fee net investment income remains
consistent with the fees incurred on pre-incentive fee net investment income for the three months ended March 31, 2017. The estimate also assumes that the capital gains incentive fees payable at the end of the 2017 calendar year will be based
on the actual cumulative realized capital gains net of cumulative realized losses and unrealized capital depreciation as of December 31, 2017, which we believe is consistent with no capital gains incentive fees payable as of March 31,
2017.

The incentive fee consists of two parts:

The first, payable quarterly in arrears, equals 20.0% of our pre-incentive fee net investment income, expressed as a rate of return on
the value of our net assets, (including interest that is accrued but not yet received in cash), subject to a 2.0% quarterly (8.0% annualized) hurdle rate and a catch-up provision measured as of the end of each calendar quarter. Under
this provision, in any calendar quarter, our investment advisor receives no incentive fee until our pre-incentive fee net investment income equals the hurdle rate of 2.0% but then receives, as a catch-up, 100.0% of our pre-incentive fee
net investment income with respect to that portion of such pre-incentive fee net

investment income, if any, that exceeds the hurdle rate but is less than 2.5%. The effect of this provision is that, if pre-incentive fee net investment income exceeds 2.5% in any calendar
quarter, our investment advisor will receive 20.0% of our pre-incentive fee net investment income as if a hurdle rate did not apply.

The second part, payable annually in arrears, equals 20.0% of our realized capital gains net of realized capital losses and unrealized capital depreciation, if any, on a cumulative basis from inception
through the end of the fiscal year (or upon the termination of the Investment Advisory Agreement, as of the termination date), less the aggregate amount of any previously paid capital gain incentive fees. We accrue, but do not pay, a capital gains
incentive fee in connection with any net unrealized capital appreciation, as appropriate. For the three months ended March 31, 2017, we accrued $0.3 million in capital gains incentive fees in accordance with generally accepted accounting
principles.

See Management and Other AgreementsInvestment Advisory Agreement in the accompanying
prospectus.

(7)

As of March 31, 2017, we had outstanding SBA debentures of $199.3 million, and unfunded commitments from the SBA to purchase up to an additional of $51.0 million
SBA debentures. We did not have any outstanding borrowings under our Credit Facility as of March 31, 2017. The Credit Facility has a total commitment of $50.0 million. Interest payments on borrowed funds is based on estimated annual interest
and fee expenses on outstanding SBA debentures and borrowings under the Credit Facility as of March 31, 2017 with a weighted average interest rate of 3.9%. We have estimated the annual interest expense on borrowed funds and caution you that our
actual interest expense will depend on prevailing interest rates and our rate of borrowing, which may be substantially higher than the estimate provided in this table.

(8)

Other expenses represent our estimated annual operating expenses, as a percentage of net assets attributable to common shares estimated for the current year, including
professional fees, directors fees, insurance costs, expenses of our dividend reinvestment plan and payments under the Administration Agreement based on our allocable portion of overhead and other expenses incurred by our administrator. See
Management and Other AgreementsAdministration Agreement in the accompanying prospectus. Other expenses exclude interest payments on borrowed funds, and if we issue debt securities or preferred stock, interest payments on debt
securities and distributions with respect to preferred stock. We currently do not have any class of securities outstanding other than common stock. Other expenses are based on actual other expenses for the three months ended
March 31, 2017.

(9)

Total annual expenses as a percentage of consolidated net assets attributable to common stock are higher than the total annual expenses percentage would be
for a company that is not leveraged. We borrow money to leverage our net assets and increase our total assets. The Securities and Exchange Commission, or SEC, requires that the total annual expenses percentage be calculated as a
percentage of net assets (defined as total assets less indebtedness and before taking into account any incentive fees payable during the period), rather than the total assets, including assets that have been purchased with borrowed amounts. If the
total annual expenses percentage were calculated instead as a percentage of average consolidated total assets for the three months ended March 31, 2017, our total annual expenses would be 5.24% of average consolidated
total assets.

Example

The following example demonstrates the projected dollar amount of total cumulative expenses over various periods with respect to a hypothetical investment in us. In calculating the following expense
amounts, we have assumed we would have no additional leverage, that none of our assets are cash or cash equivalents and that our annual operating expenses would remain at the levels set forth in the table above. Transaction expenses are not included
in the following example.

1 year

3 years

5 years

10 years

You would pay the following expenses on a $1,000 investment, assuming a 5.0% annual return

$

87

$

252

$

404

$

739

You would pay the following expenses on a $1,000 investment, assuming a 5.0% annual return resulting entirely from net realized
capital gains (all of which is subject to our incentive fee on capital gains)

$

95

$

272

$

434

$

779

The foregoing table is to assist you in understanding the various costs and expenses that an investor in
our common stock will bear directly or indirectly. While the example assumes, as required by the SEC, a 5.0% annual return, our performance will vary and may result in a return

greater or less than 5.0%. The incentive fee under the Investment Advisory Agreement, which, assuming a 5.0% annual return, would either not be payable or have an insignificant impact on the
expense amounts shown above, is not included in the example. If we achieve sufficient returns on our investments, including through the realization of capital gains, to trigger an incentive fee of a material amount, our expenses, and returns to our
investors, would be higher. In addition, while the example assumes reinvestment of all distributions at net asset value, if our board of directors authorizes and we declare a cash dividend, participants in our dividend reinvestment plan who have not
otherwise elected to receive cash will receive a number of shares of our common stock, determined by dividing the total dollar amount of the distribution payable to a participant by the market price per share of our common stock at the close of
trading on the valuation date for the distribution. See Dividend Reinvestment Plan in the accompanying prospectus for additional information regarding our dividend reinvestment plan.

This example and the expenses in the table above should not be considered a representation of our future expenses, and actual expenses
(including the cost of debt, if any, and other expenses) may be greater or less than those shown.

This prospectus supplement and the accompanying prospectus contain forward-looking statements that involve substantial
risks and uncertainties. These forward-looking statements are not historical facts, but rather are based on current expectations, estimates and projections about us, our current and prospective portfolio investments, our industry, our beliefs, and
our assumptions. Words such as anticipates, expects, intends, plans, will, may, continue, believes, seeks, estimates,
would, should, targets, projects and variations of these words and similar expressions are intended to identify forward-looking statements. The forward-looking statements contained in this prospectus
supplement and the accompanying prospectus involve risks and uncertainties, including statements as to:



our future operating results;



our business prospects and the prospects of our portfolio companies;



the impact of investments that we expect to make;



our contractual arrangements and relationships with third parties;



the dependence of our future success on the general economy and its impact on the industries in which we invest;



the ability of our portfolio companies to achieve their objectives;



our expected financing and investments;



the size and use of proceeds of this offering;



the adequacy of our cash resources and working capital;



the timing of cash flows, if any, from the operations of our portfolio companies;



the impact of increased competition;



the ability of our investment advisor to identify suitable investments for us and to monitor and administer our investments;



the ability of our investment advisor to attract and retain highly talented professionals;



our regulatory structure and tax status;



our ability to operate as a BDC, a SBIC and a RIC;



the adequacy of our cash resources and working capital;



the timing of cash flows, if any, from the operations of our portfolio companies;

the valuation of any investments in portfolio companies, particularly those having no liquid trading market; and



our ability to recover unrealized losses.

These statements are not guarantees of future performance and are subject to risks, uncertainties and other factors, some of which are beyond our control and difficult to predict and could cause actual
results to differ materially from those expressed or forecasted in the forward-looking statements, including without limitation:



an economic downturn could impair our portfolio companies ability to continue to operate, which could lead to the loss of value in of some or all
of our investments in such portfolio companies;



a contraction of available credit and/or an inability to access the equity markets could impair our lending and investment activities;



interest rate volatility could adversely affect our results, particularly because we use leverage as part of our investment strategy;



currency fluctuations could adversely affect the results of our investments in portfolio companies with foreign operations; and



the risks, uncertainties and other factors we identify in Item 1A.Risk Factors contained in our Annual Report on Form 10-K for the year
ended December 31, 2016 and in our other filings with the SEC.

Although we believe that the
assumptions on which these forward-looking statements are based are reasonable, any of those assumptions could prove to be inaccurate, and as a result, the forward-looking statements based on those assumptions also could be inaccurate. Important
assumptions include our ability to originate new loans and investments, certain margins and levels of profitability and the availability of additional capital. In light of these and other uncertainties, the inclusion of a projection or
forward-looking statement in this prospectus should not be regarded as a representation by us that our plans and objectives will be achieved. These risks and uncertainties include those described or identified in Risk Factors and
elsewhere in the accompanying prospectus. You should not place undue reliance on these forward-looking statements, which apply only as of the date of this prospectus. The forward-looking statements and projections contained in this prospectus
supplement and accompanying prospectus are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, as amended, or the Securities Act.

We estimate that our net proceeds from the sale of 1,500,000 shares of common stock we are offering will be approximately
$ million, and approximately $ million if the underwriters option to purchase additional shares is
exercised in full, and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us. We may change the size of this offering based on demand and market conditions.

We intend to use the net proceeds of this offering to invest in lower middle-market companies in accordance with our investment objective
and strategies, to repay the outstanding indebtedness under our Credit Facility, to increase our borrowing capacity under the SBIC Debenture Program and for working capital and general corporate purposes. As of June 19, 2017, there were $11.0
million of outstanding borrowings under our Credit Facility that had an interest rate of 6.75% and a maturity date of June 16, 2018, which may be extended by mutual agreement.

Pending such use, we will invest the net proceeds of this offering primarily in cash, cash equivalents, U.S. Government securities and
other high-quality debt instruments that mature in one year or less, or temporary investments, as appropriate. These securities may have lower yields than our other investments and accordingly result in lower distributions, if any, by us
during such period. See RegulationTemporary Investments in the accompanying prospectus. Our ability to achieve our investment objective may be limited to the extent that the net proceeds from the offering, pending full investment,
are held in interest bearing deposits or other short-term instruments that produce income at a rate less than our cost of capital.

The following table sets forth our capitalization as of March 31, 2017:



on an actual basis as of March 31, 2017; and



on an as-adjusted basis giving effect to the sale of 1,500,000 shares of our common stock at a price of
$ per share, less estimated underwriting discounts and offering expenses payable by us.

This table should be read in conjunction with our Managements Discussion and Analysis of Financial Condition and Results of
Operations and our financial statements and notes thereto included in this prospectus supplement and the accompanying prospectus.

Our common stock began trading on June 21, 2011 on The Nasdaq Global Market under the symbol FDUS. Effective
January 3, 2012, our common stock is included on the Nasdaq Global Select Market. Prior to June 21, 2011, there was no established public trading market for our common stock. The following table lists the high and low closing sale price
for our common stock, and the closing sale price as a percentage of net asset value, or NAV, and the cash distributions per share that we have declared on our common stock for each fiscal quarter during the last two most recently completed fiscal
years.

Period

NAV(1)

HighClosingSalesPrice

LowClosingSalesPrice

Premium /(Discount) ofHigh SalesPrice to NAV(2)

Premium /(Discount) ofLow SalesPrice to NAV(2)

DistributionsPer Share(3)

Year ending December 31, 2017

First Quarter

$

15.80

$

17.57

$

15.88

11.2

%

0.5

%

$

0.39

Second Quarter (through June 16, 2017)

*

18.06

16.37

*

*

0.39

Year ended December 31, 2016

First Quarter

15.25

15.51

11.91

1.7

(21.9

)

0.39

Second Quarter

15.52

15.96

14.70

2.8

(5.3

)

0.39

Third Quarter

15.58

16.33

15.22

4.8

(2.3

)

0.39

Fourth Quarter

15.76

17.07

14.62

8.3

(7.2

)

0.43

Year ended December 31, 2015

First Quarter

15.18

17.02

14.40

12.1

(5.1

)

0.38

Second Quarter

15.18

16.90

14.90

11.3

(1.8

)

0.40

Third Quarter

15.12

15.51

13.65

2.6

(9.7

)

0.39

Fourth Quarter

15.17

14.80

13.11

(2.4

)

(13.6

)

0.43

(1)

Net asset value per share is determined as of the last day in the relevant quarter and therefore may not reflect the net asset value per share on the date of the high
and low sales prices. The net asset values shown are based on outstanding shares at the end of each period.

(2)

Calculated as the difference between the respective high or low closing sales price and the quarter end net asset value divided by the quarter end net asset value.

(3)

Represents the regular and special, if applicable, distribution declared in the specified quarter. We have adopted an opt out dividend reinvestment plan for
our common stockholders. As a result, if we declare a distribution, stockholders cash distributions will be automatically reinvested in additional shares of our common stock, unless they specifically opt out of the dividend
reinvestment plan so as to receive cash distributions. See Dividend Reinvestment Plan.

*

Not determinable at time of filing.

We intend to continue to pay quarterly distributions to our stockholders. Our quarterly distributions, if any, are determined by our board of directors. We have elected to be taxed as a RIC under
Subchapter M of the Code. As long as we qualify as a RIC, we will not be taxed on our investment company taxable income or net capital gain, to the extent that such income or gain is distributed, or deemed to be distributed, to stockholders on a
timely basis.

There were no deemed distributions during the years 2015 or 2016.

We may not be able to achieve operating results that will allow us to make distributions at a specific level or to increase the amount of
these distributions from time to time. If we do not

distribute a certain percentage of our income annually, we will suffer adverse tax consequences, including possible loss of our tax treatment as a RIC. We cannot assure stockholders that they
will receive any distributions at a particular level.

We have adopted a dividend reinvestment plan that provides for
reinvestment of our distributions on behalf of our stockholders, unless a stockholder elects to receive cash. As a result, if our board of directors authorizes, and we declare, a cash distribution, then our stockholders who have not opted
out of our dividend reinvestment plan will have their cash distribution automatically reinvested in additional shares of our common stock, rather than receiving the cash distribution. Under the terms of our dividend reinvestment plan,
dividends will primarily be paid in newly issued shares of common stock. However, we reserve the right to purchase shares in the open market in connection with the implementation of the plan. This feature of the plan means that, under certain
circumstances, we may issue shares of our common stock at a price below net asset value per share, which could cause our stockholders to experience dilution.

Distributions in excess of our current and accumulated profits and earnings would be treated first as a return of capital to the extent of the stockholders tax basis, and any remaining distributions
would be treated as a capital gain. The determination of the tax attributes of our distributions will be made annually as of the end of our fiscal year based upon our taxable income for the full year and distributions paid for the full year.
Therefore, a determination made on a quarterly basis may not be representative of the actual tax attributes of our distributions for a full year. Each year, a statement on Form 1099-DIV identifying the source of the distribution will be sent to our
U.S. stockholders of record. Our board of directors presently intends to declare and pay quarterly dividends. Our ability to pay dividends could be affected by future business performance, liquidity, capital needs, alternative investment
opportunities and loan covenants.

The following selected consolidated financial data of Fidus Investment Corporation and its subsidiaries, including the Funds, as of and
for the years ended December 31, 2016, 2015, 2014, 2013 and 2012, is derived from the consolidated financial statements that have been audited by RSM US LLP, our independent registered public accounting firm. The selected consolidated financial
and other data for the three months ended March 31, 2017 and other quarterly financial information is derived from our unaudited financial statements, and in the opinion of management, reflects all adjustments (consisting only of normal
recurring adjustments) that are necessary to present fairly the results of such interim periods. Interim results as of and for the three months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year
ending December 31, 2017. This financial data should be read in conjunction with our consolidated financial statements and the notes thereto and Managements Discussion and Analysis of Financial Condition and Results of
Operations included in this prospectus supplement and the accompanying prospectus.

Weighted average yields are computed using the effective interest rates for debt investments at cost as of the period end date, including accretion of original issue
discount and loan origination fees, but excluding investments on non-accrual status, if any. The weighted average yield of our debt investments is not the same as a return on investment for our stockholders but, rather, relates to a portion of our
investment portfolio and is calculated before the payment of all of our and our subsidiaries fees and expenses.

MANAGEMENTS DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
AND RESULTS OF OPERATIONS

Overview

We provide customized debt and equity financing solutions to lower middle-market companies, which we define as U.S.-based companies having revenues between $10.0 million and $150.0 million. Our investment
objective is to provide attractive risk-adjusted returns by generating both current income from our debt investments and capital appreciation from our equity related investments. Our investment strategy includes partnering with business owners,
management teams and financial sponsors by providing customized financing for ownership transactions, recapitalizations, strategic acquisitions, business expansion and other growth initiatives. We seek to maintain a diversified portfolio of
investments in order to help mitigate the potential effects of adverse economic events related to particular companies, regions or industries.

FIC was formed as a Maryland corporation on February 14, 2011. We completed our initial public offering, or IPO, in June 2011.

On June 20, 2011, FIC acquired all of the limited partnership interests of Fidus Mezzanine Capital, L.P., or Fund I, and membership
interests of Fidus Mezzanine Capital GP, LLC, its general partner, through the Formation Transactions, resulting in Fund I becoming our wholly-owned SBIC subsidiary. Immediately following the Formation Transactions, we and Fund I elected to be
treated as business development companies, or BDCs, under the 1940 Act and our investment activities have been managed by Fidus Investment Advisors, LLC, our investment advisor, and supervised by our board of directors, a majority of whom are
independent of us. On March 29, 2013, we commenced operations of a second wholly-owned subsidiary, Fund II. Fund I and Fund II are collectively referred to as the Funds.

Fund I received its SBIC license on October 22, 2007 and Fund II received its SBIC license on May 28, 2013. We plan to continue
to operate the Funds as SBICs, subject to SBA approval, and to utilize the proceeds of the sale of SBA-guaranteed debentures to enhance returns to our stockholders. We have also made, and continue to make, investments directly through FIC. We
believe that utilizing FIC and the Funds as investment vehicles provides us with access to a broader array of investment opportunities. Based on the current capitalization of the Funds, we have approximately $51.0 million of remaining borrowing
capacity under the SBIC Debenture Program and intend to fully utilize such capacity over the ensuing 12 to 18 months.

Revenues: We generate revenue in the form of interest and fee income on debt investments and capital gains and distributions, if
any, on equity investments. Our debt investments, whether in the form of mezzanine, senior secured or unitranche loans, typically have terms of five to seven years and bear interest at a fixed rate but may bear interest at a floating rate. In some
instances, we receive payments on our debt investments based on scheduled amortization of the outstanding balances. In addition, we receive repayments of some of our debt investments prior to their scheduled maturity dates, which may include
prepayment penalties. The frequency or volume of these repayments fluctuates significantly from period to period. Our portfolio activity may reflect the proceeds of sales of securities. In some cases, our investments provide for deferred interest
payments or PIK interest. The principal amount of loans and any accrued but unpaid interest generally become due at the maturity date. In addition, we may generate revenue in the form of commitment, origination, amendment, or structuring fees and
fees for providing managerial assistance. Debt investment origination fees, original issue discount and market discount or premium, if any, are capitalized, and we accrete or amortize such amounts into interest income. We record prepayment premiums
on loans as fee income. Interest and dividend income is

recorded on the accrual basis to the extent that we expect to collect such amounts. Debt investments or preferred equity securities are placed on non-accrual status when principal, interest or
dividend payments become materially past due, or when there is reasonable doubt that principal, interest or dividends will be collected. See Critical Accounting Policies and Use of EstimatesRevenue Recognition. Interest is accrued
daily based on the outstanding principal amount and the contractual terms of the debt. Dividend income is recorded as dividends are declared or at the point an obligation exists for the portfolio company to make a distribution, and is generally
recognized when received. Distributions of earnings from portfolio companies are evaluated to determine if the distribution is a distribution of earnings or a return of capital. Distributions of earnings are included in dividend income while a
return of capital is recorded as a reduction in the cost basis of the investment. Estimates are adjusted as necessary when the relevant tax forms are received from the portfolio company.

We recognize realized gains or losses on investments based on the difference between the net proceeds from the disposition and the cost
basis of the investment, without regard to unrealized gains or losses previously recognized. We record current period changes in fair value of investments that are measured at fair value as a component of the net change in unrealized appreciation
(depreciation) on investments in the consolidated statements of operations.

Expenses: All investment professionals of
our investment advisor and/or its affiliates, when and to the extent engaged in providing investment advisory and management services to us, and the compensation and routine overhead expenses allocable to personnel who provide these services to us,
are provided and paid for by our investment advisor and not by us. We bear all other out-of-pocket costs and expenses of our operations and transactions, including, without limitation, those relating to:

fees and expenses incurred by our investment advisor under the Investment Advisory Agreement or payable to third parties, including agents, consultants
or other advisors, in monitoring financial and legal affairs for us and in monitoring our investments and performing due diligence on our prospective portfolio companies or otherwise relating to, or associated with, evaluating and making
investments, including dead deal costs;

administration fees and expenses, if any, payable under the Administration Agreement (including payments under the Administration Agreement between us
and our investment advisor based upon our allocable portion of our investment advisors overhead in performing its obligations under the Administration Agreement, including rent and the allocable portion of the cost of our officers, including
our chief compliance officer, our chief financial officer, and their respective staffs);

all costs of registration and listing our shares on any securities exchange;



U.S. federal, state and local taxes;



Independent Directors fees and expenses;



costs of preparing and filing reports or other documents required by the SEC or other regulators including printing costs;



costs of any reports, proxy statements or other notices to stockholders, including printing and mailing costs;



our allocable portion of any fidelity bond, directors and officers/errors and omissions liability insurance, and any other insurance premiums;



direct costs and expenses of administration, including printing, mailing, long distance telephone, copying, secretarial and other staff, independent
auditors and outside legal costs;



proxy voting expenses; and



all other expenses reasonably incurred by us or our investment advisor in connection with administering our business.

Portfolio Composition, Investment Activity and Yield

During the three months ended March 31, 2017, we invested $55.0 million in debt and equity investments, including three new portfolio companies. These investments consisted of subordinated notes
($50.4 million, or 91.6%), senior secured loans ($0.5 million, or 0.9%), equity securities ($4.0 million, or 7.3%) and warrant securities ($0.1 million, or 0.2%). During the three months ended March 31, 2017 we received proceeds from sales or
repayments, including principal, return of capital dividends and net realized gains (losses), of $47.7 million.

During the
three months ended March 31, 2016, we invested $42.3 million in debt and equity investments, including three new portfolio companies. These investments consisted of subordinated notes ($39.3 million, or 92.9%), senior secured loans ($1.4
million, or 3.2%), and equity securities ($1.6 million, or 3.9%). During the three months ended March 31, 2016 we received proceeds from sales or repayments, including principal, return of capital dividends and net realized gains (losses), of
$31.6 million.

As of March 31, 2017, the fair value of our investment portfolio totaled $536.6 million and consisted of
55 active portfolio companies and four portfolio companies that have sold their underlying operations. As of March 31, 2017, two debt investments bore interest at a variable rate, which represented $18.0 million of our portfolio on a fair value
basis, and the remainder of our debt portfolio was comprised of fixed rate investments. Overall, the portfolio had net unrealized appreciation of $20.5 million as of March 31, 2017. As of March 31, 2017, our average active portfolio
company investment at amortized cost was $9.4 million, which excludes investments in the four portfolio companies that have sold their underlying operations.

As of December 31, 2016, the fair value of our investment portfolio totaled $524.5 million and consisted of 53 active portfolio companies and four portfolio companies that have sold their underlying
operations. As of December 31, 2016, one debt investment bore interest at a variable

rate, which represented $8.2 million of our portfolio on a fair value basis, and the remainder of our debt portfolio was comprised of fixed rate investments. Overall, the portfolio had net
unrealized appreciation of $23.9 million as of December 31, 2016. As of December 31, 2016, our average active portfolio company investment at amortized cost was $9.4 million, which excludes investments in the four portfolio companies that
have sold their underlying operations.

The weighted average yield on debt investments as of March 31, 2017 and
December 31, 2016 was 12.9% and 13.1%, respectively. The weighted average yield of our debt investments is not the same as a return on investment for our stockholders but, rather, relates to a portion of our investment portfolio and is
calculated before the payment of all of our fees and expenses. The weighted average yields were computed using the effective interest rates for debt investments at cost as of March 31, 2017 and December 31, 2016, respectively, including
the accretion of original issue discount and loan origination fees, but excluding investments on non-accrual status, if any.

The following table shows the portfolio composition by investment type at fair value and cost and as a percentage of total investments:

Fair Value

Cost

March 31, 2017

December 31, 2016

March 31, 2017

December 31, 2016

(dollars in thousands)

Subordinated notes

$

372,367

69.5

%

$

363,646

69.4

%

$

375,113

72.8

%

$

364,543

72.9

%

Senior secured loans

78,480

14.6

79,758

15.2

82,753

16.0

83,426

16.7

Equity

74,047

13.8

70,849

13.5

50,749

9.8

45,207

9.0

Warrants

11,523

2.1

10,201

1.9

7,268

1.4

7,153

1.4

Royalty rights

185







185



185



Total

$

536,602

100.0

%

$

524,454

100.0

%

$

516,068

100.0

%

$

500,514

100.0

%

The following table shows portfolio composition by geographic region at fair value and cost and as a
percentage of total investments. The geographic composition is determined by the location of the corporate headquarters of the portfolio company, which may not be indicative of the primary source of the portfolio companys business.

The following table shows the detailed industry composition of our portfolio at fair value
and cost as a percentage of total investments:

Fair Value

Cost

March 31,2017

December 31,2016

March 31,2017

December 31,2016

Aerospace & Defense Manufacturing

11.6

%

11.7

%

10.8

%

11.1

%

Healthcare Products

10.7

11.1

9.1

9.3

Information Technology Services

9.1

4.5

9.6

4.8

Healthcare Services

8.1

8.0

8.3

8.5

Business Services

6.8

7.1

7.4

7.9

Building Products Manufacturing

5.6

5.7

5.5

5.6

Transportation services

5.6

8.9

5.7

8.4

Component Manufacturing

5.4

3.5

5.6

3.7

Specialty Distribution

4.8

5.0

4.8

5.0

Vending Equipment Manufacturing

4.7

3.7

4.9

3.9

Utility Equipment Manufacturing

3.4

3.5

3.5

3.7

Packaging

3.3

3.3

3.4

3.5

Capital Equipment Manufacturing

2.8

2.9

2.9

3.0

Oil & Gas Services

2.7

2.8

2.9

2.9

Industrial Cleaning & Coatings

2.4

2.4

2.6

2.7

Promotional Products

2.3

2.4

2.3

2.4

Printing Services

2.1

2.1

2.1

2.2

Retail

1.6

1.7

1.5

1.5

Specialty Chemicals

1.6

1.6

1.7

1.8

Restaurants

1.4

1.5

1.9

1.9

Oil & Gas Distribution

1.1

1.1

1.2

1.2

Apparel Distribution

1.1

1.1

1.2

1.2

Laundry Services

0.7

1.4

0.7

1.3

Consumer Products

0.6

2.6

0.1

2.2

Electronic Components Supplier

0.5

0.4

0.3

0.3

Safety Products Manufacturing

0.0

0.0

0.0

0.0

Total

100.0

%

100.0

%

100.0

%

100.0

%

Portfolio Asset Quality

In addition to various risk management and monitoring tools, our investment advisor uses an internally developed investment rating system to characterize and monitor the credit profile and our expected
level of returns on each investment in our portfolio. We use a five-level numeric rating scale. The following is a description of the conditions associated with each investment rating:



Investment Rating 1 is used for investments that involve the least amount of risk in our portfolio. The portfolio company is performing above
expectations, the debt investment is expected to be paid in the near term and the trends and risk factors are favorable, and may include an expected capital gain.

Investment Rating 2 is used for investments that involve a level of risk similar to the risk at the time of origination. The portfolio company is
performing substantially within our expectations and the risk factors are neutral or favorable. Each new portfolio investment enters our portfolio with Investment Rating 2.



Investment Rating 3 is used for investments performing below expectations and indicates the investments risk has increased somewhat since
origination. The portfolio company requires closer monitoring, but we expect a full return of principal and collection of all interest and/or dividends.



Investment Rating 4 is used for investments performing materially below expectations and the risk has increased materially since origination. The
portfolio company has the potential for some loss of investment return, but we expect no loss of principal.



Investment Rating 5 is used for investments performing substantially below our expectations and the risks have increased substantially since
origination. We expect some loss of principal.

The following table shows the distribution of our
investments on the 1 to 5 investment rating scale at fair value and cost as of March 31, 2017 and December 31, 2016:

Fair Value

Cost

Investment Rating

March 31, 2017

December 31, 2016

March 31, 2017

December 31, 2016

(dollars in thousands)

1

$

61,312

11.4

%

$

91,705

17.5

%

$

31,866

6.2

%

$

58,967

11.8

%

2

401,197

74.8

371,506

70.9

394,783

76.5

366,697

73.3

3

51,178

9.5

38,905

7.4

56,749

11.0

44,510

8.9

4

22,374

4.2

22,085

4.2

30,524

5.9

28,194

5.6

5

541

0.1

253



2,146

0.4

2,146

0.4

Total

$

536,602

100.0

%

$

524,454

100.0

%

$

516,068

100.0

%

$

500,514

100.0

%

Based on our investment rating system, the weighted average rating of our portfolio as of March 31,
2017 and December 31, 2016 was 2.1 and 2.0, respectively, on a fair value basis.

Non-Accrual

As of March 31, 2017, we had investments in one portfolio company on non-accrual status, which had an aggregate cost and fair value
of $9.1 million and $7.1 million, respectively. As of December 31, 2016, we had no investments on non-accrual status.

For the three months ended March 31, 2017 and 2016, we recognized unrealized depreciation on non-accrual investments of $0.3 million
and $0.6 million, respectively.

Discussion and Analysis of Results of Operations

Comparison of three months ended March 31, 2017 and March 31, 2016

Investment Income

For the three months ended March 31, 2017, total investment income was $16.2 million, an increase of $1.5 million, or 10.2%, over the $14.7 million of total investment income for the three

months ended March 31, 2016. The increase was attributable to a $1.2 million increase in interest income resulting from higher average debt investment balances outstanding during the three
months ended March 31, 2017 as compared to the same period in 2016, a $0.5 million increase in dividend income due to increased levels of distributions received from equity investments during the three months ended March 31, 2017 as
compared to the same period in 2016, and partially offset by a $(0.2) million decrease in fee income during the three months ended March 31, 2017 as compared to the same period in 2016.

Expenses

For the three months ended March 31, 2017, total expenses, including income tax provision, were $8.3 million, an increase of $0.7
million or 9.2%, over the $7.6 million of total expenses, including income tax provision, for the three months ended March 31, 2016. Interest and financing expenses for both the three months ended March 31, 2017 and 2016 were $2.6 million.
The base management fee increased $0.3 million, or 15.0%, to $2.3 million for the three months ended March 31, 2017 due to higher average total assets during the three months ended March 31, 2017 as compared to the same period in 2016. The
incentive fee for the three months ended March 31, 2017 was $2.3 million, a $0.4 million, or 21.1%, increase from the $1.9 million incentive fee for the three months ended March 31, 2016, which is comprised of increases in the income and
capital gains incentive fees of $0.2 million and $0.2 million, respectively, during the three months ended March 31, 2017, as compared to the same period in 2016. The administrative service fee, professional fees and other general and
administrative expenses totaled $1.1 million for both the three months ended March 31, 2017 and 2016.

Net Investment
Income

Net investment income for the three months ended March 31, 2017 was $7.9 million, an increase of $0.8
million, or 11.3%, compared to net investment income of $7.1 million during the three months ended March 31, 2016, as a result of the $1.5 million increase in total investment income compared to only a $0.7 million increase in total expenses,
including income tax provision.

Net Increase in Net Assets Resulting From Operations

For the three months ended March 31, 2017, the total net realized gain on investments was $6.4 million. Significant realized gains
and (losses) for the three months ended March 31, 2017 are summarized below:

Portfolio Company

Realization Event

Net RealizedGain (Loss)(in millions)

Worldwide Express Operations, LLC

Sale of portfolio company

$

6.4

Total

$

6.4

For the three months ended March 31, 2016, the total net realized (loss) on investments was $0.3
million, as summarized below:

During the three months ended March 31, 2017, we recorded a net change in unrealized
depreciation on investments of $(3.4) million attributable to (i) the reversal of net unrealized appreciation of $(4.5) million related to the exit, sale or restructuring of investments, resulting in unrealized depreciation, (ii) net
unrealized depreciation of $(2.1) million on debt investments and (iii) net unrealized appreciation of $3.2 million on equity investments. During the three months ended March 31, 2016, we recorded a net change in unrealized appreciation on
investments of $0.8 million attributable to (i) the reversal of net unrealized depreciation on investments of $0.9 million related to the exit or sale of investments, resulting in unrealized appreciation, (ii) net unrealized depreciation
of $(5.9) million on debt investments and (iii) net unrealized appreciation of $5.8 million on equity investments.

During the three months ended March 31, 2017, we recorded $(1.4) million of income tax provision for realized gains on investments.
During the three months ended March 31, 2016, no income tax provision for realized gains on investments was recorded.

As
a result of these events, our net increase in net assets resulting from operations during the three months ended March 31, 2017 was $9.5 million, an increase of $2.0 million, or 26.7%, compared to a net increase in net assets resulting from
operations of $7.5 million during the three months ended March 31, 2016.

Liquidity and Capital Resources

As of March 31, 2017, we had $19.1 million in cash and cash equivalents and our net assets totaled $354.8 million.
We believe that our current cash and cash equivalents on hand, our continued access to SBA-guaranteed debentures, availability under our Credit Facility and our anticipated cash flows from operations will provide adequate capital resources with
which to operate and finance our investment business and make distributions to our stockholders for at least the next 12 months. We intend to generate additional cash primarily from the future offerings of securities (including the ATM Program) and
future borrowings, as well as cash flows from operations, including income earned from investments in our portfolio companies. On both a short-term and long-term basis, our primary use of funds will be investments in portfolio companies and cash
distributions to our stockholders. During the three months ended March 31, 2017, we repaid $24.8 million of SBA debentures which would have matured on March 1, 2018. Our remaining outstanding SBA debentures continue to mature in 2018 and
subsequent years through 2027, which will require repayment on or before the respective maturity dates.

Cash Flows

For the three months ended March 31, 2017, we experienced a net decrease in cash and cash equivalents in the amount
of $38.0 million. During that period, we used $4.7 million of cash for operating activities, which included the funding of $55.0 million of investments, which were offset by proceeds received from sales and repayments of investments of $47.7
million. During the same period, we repaid SBA debentures of $24.8 million and paid cash dividends to stockholders of $8.6 million.

For the three months ended March 31, 2016, we experienced a net decrease in cash and cash equivalents in the amount of $18.6 million. During that period, we used $8.4 million of cash for operating
activities, primarily for the funding of $42.3 million of investments, which was partially offset by the proceeds from sales and repayments of investments of $31.6 million. During the same period, we received proceeds from the issuance of SBA
debentures of $0.5 million, which were offset by net repayment of borrowings under the Credit Facility of $4.5 million, cash dividends paid to stockholders of $6.2 million and the payment of deferred financing costs of less than $0.1 million.

We anticipate that we will continue to fund our investment activities on a long-term basis through a combination of additional debt and
equity capital.

The Funds are licensed SBICs, and have the ability to issue debentures guaranteed by the SBA at favorable
interest rates. Under the Small Business Investment Act and the SBA rules applicable to SBICs, an SBIC can have outstanding at any time debentures guaranteed by the SBA in an amount up to twice its regulatory capital. The SBA regulations currently
limit the amount that is available to be borrowed by any SBIC and guaranteed by the SBA to 300.0% of an SBICs regulatory capital or $150.0 million, whichever is less. For three or more SBICs under common control, the maximum amount of
outstanding SBA debentures cannot exceed $350.0 million. SBA debentures have fixed interest rates that approximate prevailing 10-year Treasury Note rates plus a spread and have a maturity of ten years with interest payable semi-annually. The
principal amount of the SBA debentures is not required to be paid before maturity but may be pre-paid at any time. As of March 31, 2017, Fund I had $125.3 million of outstanding SBA debentures and cannot issue additional SBA debentures. As of
March 31, 2017, Fund II had $74.0 million of outstanding SBA debentures. As of March 31, 2017, Fund II had the capacity to issue up to an additional $51.0 million of SBA debentures. Subject to SBA regulatory requirements and approval, we
may access up to $99.7 million of additional SBA debentures under the SBIC Debenture Program. For more information on the SBA debentures, please see Note 6 to our consolidated financial statements.

In June 2014, we entered into the Credit Facility to provide additional funding for our investment and operational activities. The Credit
Facility, which matures on June 16, 2018, had an initial commitment of $30.0 million and an accordion feature that allows for an increase in the total commitments up to $75.0 million, subject to certain customary conditions. The Credit Facility
is secured by substantially all of our assets, excluding the assets of the Funds.

On December 19, 2014, we amended the
Credit Facility to (i) increase the commitment from $30.0 million to $50.0 million (ii) allow FIC to buy-back up to $10.0 million of our common stock subject to the satisfaction of specified financial covenants and conditions. The Credit
Facility continues to have an accordion feature which allows for an increase in the total commitment up to $75.0 million.

Amounts available to borrow under the Credit Facility are subject to a minimum borrowing/collateral base that applies an advance rate to
certain portfolio investments. We are subject to limitations with respect to the investments securing the Credit Facility, including, but not limited to, restrictions on sector concentrations, loan size, transferability, payment frequency and status
and collateral interests, as well as restrictions on portfolio company leverage, which may also affect the borrowing base and therefore amounts available to borrow.

Borrowings under the Credit Facility bear interest, subject to our election, on a per annum basis equal to (i) the alternate base rate plus 2.5% or (ii) the applicable LIBOR, which varies
depending on the period of the borrowing under the Credit Facility, plus 3.5%. The alternate base rate is equal to the greater of (i) prime rate, (ii) the federal funds rate plus 0.5% or (iii) the three-month LIBOR plus 1.0%. We pay a
commitment fee ranging from 0.5% to 1.0% per annum based on the size of the unused portion of the Credit Facility.

We
have made customary representations and warranties and are required to comply with various covenants, reporting requirements and other customary requirements for similar credit facilities. These covenants are subject to important limitations and
exceptions that are described in

the documents governing the Credit Facility. As of March 31, 2017, we were in compliance with all covenants of the Credit Facility and there were no borrowings outstanding under the Credit
Facility.

As of March 31, 2017, the weighted average interest rate for all SBA debentures and borrowings outstanding
under the Credit Facility was 3.9%.

As a BDC, we are generally required to meet a coverage ratio of total assets to total
senior securities, which include borrowings and any preferred stock we may issue in the future, of at least 200.0%. This requirement limits the amount that we may borrow. We have received exemptive relief from the Securities and Exchange Commission,
or the SEC, to allow us to exclude any indebtedness guaranteed by the SBA and issued by the Funds from the 200.0% asset coverage requirements, which, in turn, will enable us to fund more investments with debt capital.

As a BDC, we are generally not permitted to issue and sell our common stock at a price below net asset value per share. We may, however,
sell our common stock, or warrants, options or rights to acquire our common stock, at a price below the then-current net asset value per share of our common stock if our board of directors, including Independent Directors, determines that such sale
is in the best interests of us and our stockholders, and if our stockholders approve such sale. On June 15, 2017, our stockholders voted to allow us to sell or otherwise issue common stock at a price below net asset value per share for a period
of one year ending on the earlier of June 15, 2018 or the date of our 2018 Annual Meeting of Stockholders. Our stockholders specified that the cumulative number of shares sold in each offering during the one-year period ending on the earlier of
June 15, 2018 or the date of our 2018 Annual Meeting of Stockholders may not exceed 25.0% of our outstanding common stock immediately prior to each such sale.

Stock repurchase plan

We have an open market stock repurchase program, or
the Program, under which we may acquire up to $5.0 million of our outstanding common stock. Under the Program, we may, but are not obligated to, repurchase outstanding common stock in the open market from time to time provided that we comply with
the prohibitions under our insider trading policies and the requirements of Rule 10b-18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, including certain price, market value and timing constraints. The timing, manner, price
and amount of any share repurchases will be determined by our management, in its discretion, based upon the evaluation of economic and market conditions, stock price, capital availability, applicable legal and regulatory requirements and other
corporate considerations. On November 1, 2016, the Board extended the Program through December 31, 2017, or until the approved dollar amount has been used to repurchase shares. The Program does not require us to repurchase any
specific number of shares and the Company cannot assure that any shares will be repurchased under the Program. The Program may be suspended, extended, modified or discontinued at any time. We did not make any repurchases of common stock during the
three months ended March 31, 2017 or 2016.

Critical Accounting Policies and Use of Estimates

The preparation of financial statements in accordance with GAAP requires management to make certain estimates and assumptions affecting
amounts reported in the financial statements. We have identified investment valuation and revenue recognition as our most critical accounting estimates. We continuously evaluate our estimates, including those related to the matters described below.
These estimates are based on the information that is currently available to us and on various other assumptions that we believe to be reasonable under the circumstances. Actual

results could differ materially from those estimates under different assumptions or conditions. A discussion of our critical accounting policies follows.

Valuation of Portfolio Investments

As a BDC, we report our assets and liabilities at fair value at all times consistent with GAAP and the 1940 Act. Accordingly, we are required to periodically determine the fair value of all of our
portfolio investments.

Our investments generally consist of illiquid securities including debt and equity investments in
lower middle-market companies. Investments for which market quotations are readily available are valued at such market quotations. Because we expect that there will not be a readily available market for substantially all of the investments in our
portfolio, we value substantially all of our portfolio investments at fair value as determined in good faith by our board of directors using a documented valuation policy and consistently applied valuation process. Due to the inherent uncertainty of
determining the fair value of investments that do not have a readily available market value, the fair value of our investments may differ significantly from the values that would have been used had a readily available market value existed for such
investments, and the difference could be material.

With respect to investments for which market quotations are not readily
available, our board of directors undertakes a multi-step valuation process each quarter, as described below:



our quarterly valuation process begins with each portfolio company or investment being initially evaluated and rated by the investment professionals of
our investment advisor responsible for the portfolio investment;



preliminary valuation conclusions are then documented and discussed with the investment committee of our investment advisor;



our board of directors engages one or more independent valuation firm(s) to conduct independent appraisals of a selection of our portfolio investments
for which market quotations are not readily available. Each portfolio company investment is generally appraised by the valuation firm(s) at least once every calendar year and each new portfolio company investment is appraised at least once in the
twelve-month period following the initial investment. In certain instances, we may determine that it is not cost-effective, and as a result it is not in our stockholders best interest, to request the independent appraisal of certain portfolio
company investments. Such instances include, but are not limited to, situations where we determine that the fair value of the portfolio company investment is relatively insignificant to the fair value of the total portfolio. Our board of directors
consulted with the independent valuation firm(s) in arriving at our determination of fair value for 16 and 13 of our portfolio company investments representing 29.8% and 30.5% of the total portfolio investments at fair value (exclusive of new
portfolio company investments made during the three months ended March 31, 2017 and December 31, 2016, respectively) as of March 31, 2017 and December 31, 2016, respectively;



the audit committee of our board of directors reviews the preliminary valuations of our investment advisor and of the independent valuation firm(s) and
responds and supplements the valuation recommendations to reflect any comments; and



our board of directors discusses the valuations and determines the fair value of each investment in our portfolio in good faith, based on the input of
our investment advisor, the independent valuation firm(s) and the audit committee.

In making the good faith determination of the value of portfolio investments, we start with
the cost basis of the security. The transaction price is typically the best estimate of fair value at inception. When evidence supports a subsequent change to the carrying value from the original transaction price, adjustments are made to reflect
the expected exit values.

Consistent with the policies and methodologies adopted by our board of directors, we perform
detailed valuations of our debt and equity investments, including an analysis on the Companys unfunded loan commitments, using both the market and income approaches as appropriate. Under the market approach, we typically use the enterprise
value methodology to determine the fair value of an investment. There is no one methodology to estimate enterprise value and, in fact, for any one portfolio company, enterprise value is generally best expressed as a range of values, from which we
derive a single estimate of enterprise value. Under the income approach, we typically prepare and analyze discounted cash flow models to estimate the present value of future cash flows of either an individual debt investment or of the underlying
portfolio company itself.

We evaluate investments in portfolio companies using the most recent portfolio company financial
statements and forecasts. We also consult with the portfolio companys senior management to obtain further updates on the portfolio companys performance, including information such as industry trends, new product development and other
operational issues.

For our debt investments, including senior secured loans and subordinated notes, the primary valuation
technique used to estimate the fair value is the discounted cash flow method. However, if there is deterioration in credit quality or a debt investment is in workout status, we may consider other methods in determining the fair value, including the
value attributable to the debt investment from the enterprise value of the portfolio company or the proceeds that would be received in a liquidation analysis. Our discounted cash flow models estimate a range of fair values by applying an appropriate
discount rate to the future cash flow streams of our debt investments, based on future interest and principal payments as set forth in the associated loan agreements. We prepare a weighted average cost of capital for use in the discounted cash flow
model for each investment, based on factors including, but not limited to: current pricing and credit metrics for similar proposed or executed investment transactions of private companies; the portfolio companys historical financial results
and outlook; and the portfolio companys current leverage and credit quality as compared to leverage and credit quality as of the date the investment was made. We may also consider the following factors when determining the fair value of debt
investments: the portfolio companys ability to make future scheduled payments; prepayment penalties and other fees; estimated remaining life; the nature and realizable value of any collateral securing such debt investment; and changes in the
interest rate environment and the credit markets that generally may affect the price at which similar investments may be made. We estimate the remaining life of our debt investments to generally be the legal maturity date of the instrument, as we
generally intend to hold loans to maturity. However, if we have information available to us that the loan is expected to be repaid in the near term, we would use an estimated remaining life based on the expected repayment date.

For our equity investments, including equity securities and warrants, we generally use a market approach, including valuation
methodologies consistent with industry practice, to estimate the enterprise value of portfolio companies. Typically, the enterprise value of a private company is based on multiples of EBITDA, net income, revenues, or in limited cases, book value. In
estimating the enterprise value of a portfolio company, we analyze various factors consistent with industry practice, including but not limited to original transaction multiples, the portfolio companys historical and projected financial
results, applicable market trading and transaction comparables, applicable market yields and leverage levels, the nature and realizable value of any collateral, the markets in which the portfolio company does business, and comparisons of financial
ratios of peer

companies that are public. Where applicable, we consider our ability to influence the capital structure of the portfolio company, as well as the timing of a potential exit.

We may also utilize an income approach when estimating the fair value of our equity securities, either as a primary methodology if
consistent with industry practice or if the market approach is otherwise not applicable, or as a supporting methodology to corroborate the fair value ranges determined by the market approach. We typically prepare and analyze discounted cash flow
models based on projections of the future free cash flows (or earnings) of the portfolio company. We consider various factors, including but not limited to the portfolio companys projected financial results, applicable market trading and
transaction comparables, applicable market yields and leverage levels, the markets in which the portfolio company does business, and comparisons of financial ratios of peer companies that are public.

The fair value of our royalty rights are calculated based on projected future cash flows and the specific provisions contained in the
pertinent royalty agreement. The determination of the fair value of such royalty rights is not a significant component of our valuation process.

Determination of fair value involves subjective judgments and estimates. Accordingly, the notes to our consolidated financial statements express the uncertainties with respect to the possible effect of
such valuations, and any changes in such valuations, on the consolidated financial statements.

Revenue Recognition

Investments and related investment income. Realized gains or losses on investments are recorded upon the sale or
disposition of a portfolio investment and are calculated as the difference between the net proceeds from the sale or disposition and the cost basis of the investment, without regard to unrealized appreciation or depreciation previously recognized.
Net change in unrealized appreciation or depreciation on the consolidated statements of operations includes changes in the fair value of investments from the prior period, as determined by our board of directors through the application of our
valuation policy, as well as reclassifications of any prior period unrealized appreciation or depreciation on exited investments to realized gains or losses on investments.

Interest and dividend income. Interest and dividend income are recorded on the accrual basis to the extent that we expect to collect such amounts. Interest is accrued daily based on the outstanding
principal amount and the contractual terms of the debt. Dividend income is recorded as dividends are declared or at the point an obligation exists for the portfolio company to make a distribution, and is generally recognized when received.
Distributions from portfolio companies are evaluated to determine if the distribution is a distribution of earnings or a return of capital. Distributions of earnings are included in dividend income while a return of capital is recorded as a
reduction in the cost basis of the investment. Estimates are adjusted as necessary when the relevant tax forms are received from the portfolio company.

Payment-in-kind interest. Certain of our investments contain a PIK income provision. The PIK income, computed at the contractual rate specified in the applicable investment agreement, is added to
the principal balance of the investment, rather than being paid in cash, and recorded as interest or dividend income, as applicable, on the consolidated statements of operations. Generally, PIK can be paid-in-kind or all in cash. We stop accruing
PIK income when there is reasonable doubt that PIK income will be collected. PIK income is included in our taxable income and, therefore, affects the amount we are required to pay to our stockholders in the form of dividends in order to maintain our
tax treatment as a RIC and to avoid paying corporate federal income tax, even though we have not yet collected the cash.

Non-accrual. When there is reasonable doubt that principal, interest or dividends
will be collected, loans or preferred equity investments are placed on non-accrual status and we will generally cease recognizing interest or dividend income. Interest and dividend payments received on non-accrual investments may be recognized as
interest or dividend income or applied to the investment principal balance based on managements judgment. Non-accrual investments are restored to accrual status when past due principal, interest or dividends are paid and, in managements
judgment, are likely to remain current.

Warrants. In connection with our debt investments, we will sometimes receive
warrants or other equity-related securities (Warrants). We determine the cost basis of Warrants based upon their respective fair values on the date of receipt in proportion to the total fair value of the debt and Warrants received. Any resulting
difference between the face amount of the debt and its recorded fair value resulting from the assignment of value to the Warrants is treated as original issue discount, or OID, and accreted into interest income using the effective interest method
over the term of the debt investment.

Fee income. All transaction fees earned in connection with our investments are
recognized as fee income. Such fees typically include fees for services, including structuring and advisory services, provided to portfolio companies. We recognize income from fees for providing such structuring and advisory services when the
services are rendered or the transactions are completed. Upon the prepayment of a loan or debt security, any prepayment penalties are recorded as fee income when earned.

We also typically receive loan origination or closing fees in connection with investments. Such loan origination and closing fees are capitalized as unearned income and offset against investment cost
basis on our consolidated statements of assets and liabilities and accreted into income over the term of the investment.

Recently Issued
Accounting Standards

In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards
Update (ASU) 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in Revenue Recognition (Topic 605). Under the new guidance, an entity should recognize revenue
to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14, which
defers the effective date of ASU 2014-09, such that the guidance is effective for annual and interim reporting periods beginning after December 15, 2017 and early application is permitted only for annual reporting periods beginning after
December 15, 2016, including interim reporting periods within that reporting period. We are currently evaluating the impact this ASU will have on our consolidated financial position or disclosures, but we do not expect the impact to be
material.

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash
Receipts and Cash Payments, which addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash
flows. This guidance is effective for annual and interim reporting periods beginning after December 15, 2017 and early adoption is permitted, including adoption in an interim period. We are currently evaluating the impact this ASU will have on
our consolidated financial position or disclosures.

In December 2016, the FASB issued ASU 2016-19, Technical Corrections
and Improvements, which includes minor corrections and clarifications that affect a wide variety of topics in the Accounting Standards Codification, including an amendment to Topic 820, Fair Value

Measurement, which clarifies the difference between a valuation approach and a valuation technique when applying the guidance of that Topic. The amendment also requires an entity to
disclose when there has been a change in either or both a valuation approach and/or a valuation technique. The transition guidance for the Topic 820 amendment must be applied prospectively because it could potentially involve the use of hindsight
that includes fair value measurements. The guidance is effective for fiscal years, and interim periods within those fiscal years, for all entities beginning after December 15, 2016. We adopted this ASU effective January 1, 2017, and the
amendments do not have a material effect on our consolidated financial position or disclosures.

Off-Balance Sheet Arrangements

We may be a party to financial instruments with off-balance sheet risk in the normal course of business to meet the
financial needs of our portfolio companies. We had off-balance sheet arrangements consisting of outstanding commitments to fund various undrawn revolving loans and other credit facilities totaling $6.1 million and $6.6 million as of March 31,
2017 and December 31, 2016, respectively. Such outstanding commitments are summarized in the following table (dollars in thousands):

March 31, 2017

December 31, 2016

Portfolio CompanyInvestment

TotalCommitment

UnfundedCommitment

TotalCommitment

UnfundedCommitment

FAR Research Inc.Revolving Loan

$

1,750

$

1,614

$

1,750

$

1,614

Inflexxion, Inc.Revolving Loan

500

350

500

350

inthinc Technology Solutions, Inc.Subordinated Note

5,000

1,000

5,000

1,000

Lightning Diversion Systems, LLCRevolving Loan

250

250

250

250

Oaktree Medical Centre, P.C.Revolving Loan

2,500



2,500



Safety Products Group, LLCCommon Equity

2,852

2,852

2,852

2,852

SES Investors, LLCRevolving Loan

1,500



1,500

500

Total

$

14,352

$

6,066

$

14,352

$

6,566

Additional detail for each of the commitments above is provided in the Companys consolidated
schedules of investments.

Related Party Transactions

We have entered into a number of business relationships with affiliated or related parties, including the following:



In connection with the Formation Transactions, Fund I terminated its management services agreement with Fidus Capital, LLC and we entered into the
Investment Advisory Agreement with Fidus Investment Advisors, LLC, as our investment advisor. The investment professionals of Fidus Investment Advisors, LLC were also the investment professionals of Fidus Capital, LLC. We entered into the Investment
Advisory Agreement with Fidus Investment Advisors, LLC to manage our day-to-day operating and investing activities. We pay our investment advisor a fee for its services under the Investment

Edward H. Ross, our Chairman and Chief Executive Officer, and Thomas C. Lauer, our President, are managers of Fidus Investment Advisors,
LLC. In May 2015, Fidus Investment Advisors, LLC entered into a combination with Fidus Partners, LLC (the Combination), by which members of Fidus Investment Advisors LLC and Fidus Partners, LLC (Partners) contributed all of
their respective membership interest in Fidus Investment Advisors LLC and Partners to a newly formed limited liability company, Fidus Group Holdings, LLC (Holdings). As a result, Fidus Investment Advisors LLC is a wholly-owned subsidiary
of Holdings, which is a newly formed limited liability company organized under the laws of Delaware.



We entered into the Administration Agreement with Fidus Investment Advisors, LLC to provide us with the office facilities and administrative services
necessary to conduct day-to-day operations. See Note 5 to our consolidated financial statements.



We entered into a license agreement with Fidus Partners, LLC, pursuant to which Fidus Partners, LLC has granted us a non-exclusive, royalty-free
license to use the name Fidus.

In connection with the IPO and our election to be regulated as a
BDC, we applied for and received exemptive relief from the SEC on March 27, 2012 to allow us to take certain actions that would otherwise be prohibited by the 1940 Act, as applicable to BDCs. The relief permits FIC and Fund I, each of which has
elected to be treated as a BDC, to operate effectively as one company, specifically allowing them to: (1) engage in certain transactions with each other; (2) invest in securities in which the other is or proposes to be an investor;
(3) file consolidated reports with the Commission; and (4) be subject to modified consolidated asset coverage requirements for senior securities issued by a BDC and its SBIC subsidiary. Fund II has not elected to be treated as a BDC and is
not party to this exemptive relief. The fourth exemption described above allows us to exclude any indebtedness guaranteed by the SBA and issued by Fund I from the 200.0% asset coverage requirements applicable to us. Effective September 30,
2014, any SBA debentures issued by Fund II are not considered senior securities for purposes of the 200.0% asset coverage requirements.

While we may co-invest with investment entities managed by our investment advisor or its affiliates, to the extent permitted by the 1940 Act and the rules and regulations thereunder, the 1940 Act imposes
significant limits on co-investment. The SEC staff has granted us relief sought in an exemptive application that expands our ability to co-invest in portfolio companies with other funds managed by our investment advisor or its affiliates
(Affiliated Funds) in a manner consistent with our investment objective, positions, policies, strategies and restrictions as well as regulatory requirements and other pertinent factors, subject to compliance with certain conditions (the
Order). Pursuant to the Order, we are permitted to co-invest with our affiliates if a required majority (as defined in Section 57(o) of the 1940 Act) or our independent directors make certain conclusions in connection
with a co-investment transaction, including that (1) the terms of the transactions, including the consideration to be paid, are reasonable and fair to us and our stockholders and do not involve overreaching by us or our stockholders on the part
of any person concerned, and (2) the transaction is consistent with the interests of our stockholders and is consistent with our investment objective and strategies.

In addition, we, Fund I and our investment advisor have each adopted a joint code of ethics pursuant to Rule 17j-1 under the 1940 Act that governs the conduct of our and our investment advisors
officers, directors and employees. Additionally, our investment advisor has adopted a

code of ethics pursuant to rule 240A-1 under the 1940 Act and in accordance with Rule 17j-1(c). We, and Fund I, have also adopted a code of business conduct that is applicable to all officers,
directors and employees of Fidus and our investment advisor. Our officers and directors also remain subject to the duties imposed by both the 1940 Act and the Maryland General Corporation Law.

Recent Developments

On
April 7, 2017, we sold our equity investment in Anatrace Products, LLC for a realized gain of $0.9 million.

On
May 1, 2017, the Board declared a regular quarterly dividend of $0.39 per share payable on June 23, 2017 to stockholders of record as of June 9, 2017.

Quantitative and Qualitative Disclosures About Market Risk.

We are
subject to financial market risks, including changes in interest rates. Changes in interest rates affect both our cost of funding and the valuation of our investment portfolio. Our risk management systems and procedures are designed to identify and
analyze our risk, to set appropriate policies and limits and to continually monitor these risks and limits by means of reliable administrative and information systems and other policies and programs. In the future, our investment income may also be
affected by changes in various interest rates, including LIBOR and prime rates, to the extent of any debt investments that include floating interest rates. As of March 31, 2017 and December 31, 2016, two and one debt investments,
respectively, bore interest at variable rates, which represented $18.0 million and $8.2 million of our portfolio on a fair value basis, respectively, and the remainder of our debt portfolio was comprised entirely of fixed rate investments. Assuming
that the consolidated statements of assets and liabilities as of March 31, 2017 and December 31, 2016 were to remain constant, a hypothetical 100 basis point change in interest rates would not have a material effect on our level of
interest income from debt investments. Our pooled SBA debentures bear interest at fixed rates. Our Credit Facility bears interest, subject to our election, on a per annum basis equal to (i) the alternate base rate plus 2.5% or (ii) the
applicable LIBOR, which varies depending on the period of the borrowing under the Credit Facility, plus 3.5%. The alternate base rate is equal to the greater of (i) prime rate, (ii) the federal funds rate plus 0.5% or (iii) the
three-month LIBOR plus 1.0%.

Because we currently borrow, and plan to borrow in the future, money to make investments, our
net investment income is dependent upon the difference between the rate at which we borrow funds and the rate at which we invest the funds borrowed. Accordingly, there can be no assurance that a significant change in market interest rates will not
have a material adverse effect on our net investment income. In periods of rising interest rates, our cost of funds would increase, which could reduce our net investment income if there is not a corresponding increase in interest income generated by
our investment portfolio.

We and the underwriters named below have entered into an underwriting agreement with respect to the shares being offered. Subject to
certain conditions, each underwriter has severally agreed to purchase the number of shares indicated in the following table. Raymond James & Associates, Inc. is the representative of the underwriters.

Underwriter

Number ofShares

Raymond James & Associates, Inc.

Robert W. Baird & Co. Incorporated

Keefe, Bruyette & Woods, Inc.

Total

1,500,000

The underwriting agreement provides that the obligations of the underwriters to pay for and accept
delivery of the shares of common stock offered hereby are subject to the approval of certain legal matters by their counsel and to certain other conditions. The underwriters are severally obligated to take and pay for all shares of common stock
offered hereby (other than those covered by the underwriters option described below) if any such shares are taken. We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act.

Our common stock is listed on the Nasdaq Global Select Market under the symbol FDUS.

Option to Purchase Additional Securities

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus supplement, to purchase up to an aggregate of 225,000 additional shares of common stock at the
public offering price plus accrued dividends, if any, set forth on the cover page hereof, less the underwriting discount. To the extent such option is exercised, each underwriter will become obligated, subject to certain conditions, to purchase
approximately the same percentage of such additional shares of common stock as the number set forth next to such underwriters name in the preceding table bears to the total number of shares set forth next to the names of all underwriters in
the preceding table.

Lock-Up Agreements

We, and certain of our executive officers and directors, have agreed, subject to certain exceptions, not to issue, sell, offer to sell, contract or agree to sell, hypothecate, pledge, transfer, grant any
option to purchase, establish an open put equivalent position or otherwise dispose of or agree to dispose of directly or indirectly, any shares of our common stock, or any securities convertible into or exercisable or exchangeable for any shares of
our common stock or any right to acquire shares of our common stock, for 60 days from the date of this prospectus supplement, subject to extension upon material announcements or earnings releases. The representative, at any time and without notice,
may release all or any portion of the common stock subject to the foregoing lock-up agreements.

The underwriters initially propose to offer the shares directly to the public at the public offering price set forth on the cover page of this prospectus supplement and to certain dealers at a price that
represents a concession not in excess of $ per share below the public offering price. After the initial public offering of the shares, the offering price and other selling terms
may be changed by the underwriters.

The following table provides information regarding the per share and total underwriting
discount that we are to pay to the underwriters. These amounts are shown assuming both no exercise and full exercise of the underwriters option to purchase up to 225,000 additional shares from us.

PerShare

Total WithoutExercise ofUnderwritersOption

Total withFull Exercise ofUnderwritersOption

Underwriting discount payable by us on shares sold to the public

$

$

$

We estimate that the total expenses of the offering payable by us, excluding the underwriting discount,
will be approximately $200,000.

A prospectus supplement in electronic format may be made available on the web sites
maintained by one or more of the underwriters, or selling group members, if any, participating in this offering. The representative may agree to allocate a number of shares to underwriters and selling group members for the sale to their online
brokerage account holders. Internet distributions will be allocated by the underwriters and selling group members that will make Internet distributions on the same basis as other allocations. The representative may agree to allocate a number of
shares to underwriters for sale to their online brokerage account holders.

Price Stabilization, Short Positions and Penalty Bids

In connection with this offering, the underwriters may purchase and sell shares of our common stock in the open market.
These transactions may include over-allotment, syndicate covering transactions and stabilizing transactions. An over-allotment involves syndicate sales of shares in excess of the number of shares to be purchased by the underwriters in the offering,
which creates a syndicate short position. Syndicate covering transactions involve purchases of shares in the open market after the distribution has been completed in order to cover syndicate short positions.

Stabilizing transactions consist of some bids or purchases of shares of our common stock made for the purpose of preventing or slowing a
decline in the market price of the shares while the offering is in progress.

In addition, the underwriters may impose penalty
bids, under which they may reclaim the selling concession from a syndicate member when the shares of our common stock originally sold by that syndicate member are purchased in a stabilizing transaction or syndicate covering transaction to cover
syndicate short positions.

Similar to other purchase transactions, these activities may have the effect of raising or
maintaining the market price of the common stock or preventing or slowing a decline in the market price of the common stock. As a result, the price of the common stock may be higher than

the price that might otherwise exist in the open market. Except for the sale of shares of our common stock in this offering, the underwriters may carry out these transactions on the Nasdaq Global
Select Market, in the over-the-counter market or otherwise.

Neither the underwriters nor we make any representation or
prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of the shares. In addition, neither the underwriters nor we make any representation that the underwriters will engage in these
transactions or that these transactions, once commenced, will not be discontinued without notice.

Passive Market Making

In connection with the offering, the underwriters may engage in passive market making transactions in the common stock on the Nasdaq
Global Select Market in accordance with Rule 103 of Regulation M under the Exchange Act during the period before the commencement of offers or sales of common stock and extending through the completion of distribution. A passive market maker must
display its bids at a price not in excess of the highest independent bid of the security. However, if all independent bids are lowered below the passive market makers bid that bid must be lowered when specified purchase limits are exceeded.

Conflicts of Interest

The underwriters and/or their affiliates from time to time provide and may in the future provide investment banking, commercial banking and financial advisory services to us, for which they have received
and may receive customary compensation.

In addition, the underwriters and/or their affiliates may from time to time refer
investment banking clients to us as potential portfolio investments. If we invest in those clients, we may utilize net proceeds from this offering to fund such investments, and the referring underwriter or its affiliate may receive placement fees
from its client in connection with such financing, which placement fees may be paid out of the amount funded by us.

Certain legal matters will be passed upon for us by Eversheds Sutherland (US) LLP. Eversheds Sutherland (US) LLP also
represents our investment advisor. Certain legal matters will be passed upon for the underwriters by Morrison & Foerster LLP, New York, New York.

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The consolidated financial statements, the related senior securities table and the effectiveness of internal control over financial
reporting appearing in the accompanying prospectus and registration statement have been audited by RSM US LLP, an independent registered public accounting firm located at One South Wacker Drive, Suite 800, Chicago, Illinois 60606, as stated in their
reports appearing elsewhere herein, and are included in reliance upon such reports and upon the authority of such firm as experts in accounting and auditing.

We have filed with the SEC a registration statement on Form N-2, together with all amendments and related exhibits, under the Securities
Act, with respect to the securities offered by this prospectus. The registration statement contains additional information about us and the securities being offered by this prospectus.

We file with or submit to the SEC annual, quarterly and current periodic reports, proxy statements and other information meeting the
informational requirements of the Exchange Act. You may inspect and copy these reports, proxy statements and other information, as well as the registration statement and related exhibits and schedules, at the SECs Public Reference Room at 100
F Street, N.E., Washington, D.C. 20549-0102. You may obtain information on the operation of the Public Reference Room by calling the SEC at (202) 551-8090. We maintain a website at http://www.fdus.com and intend to make all of our
annual, quarterly and current reports, proxy statements and other publicly filed information available, free of charge, on or through our website. Information contained on our website is not incorporated into this prospectus supplement, and you
should not consider information on our website to be part of this prospectus supplement. You may also obtain such information by contacting us in writing at 1603 Orrington Avenue, Suite 1005, Evanston, Illinois 60201, Attention: Investor Relations.
The SEC maintains a website that contains reports, proxy and information statements and other information we file with the SEC at http://www.sec.gov. Copies of these reports, proxy and information statements and other information may also be
obtained, after paying a duplicating fee, by electronic request at the following e-mail address: publicinfo@sec.gov, or by writing the SECs Public Reference Section, 100 F Street, N.E., Washington, D.C. 20549-0102.

PRIVACY NOTICE

We are committed to maintaining the privacy of our stockholders and to safeguarding their nonpublic personal information. The following information is provided to help you understand what personal
information we collect, how we protect that information and why, in certain cases, we may share information with select other parties.

From time to time, we may receive nonpublic personal information relating to our stockholders. We do not disclose nonpublic personal information about our stockholders or former stockholders to anyone,
except as required by law or as is necessary in order to service stockholder accounts (for example, to a transfer agent or third-party administrator).

We restrict access to nonpublic personal information about our stockholders to employees of our investment advisor, its affiliates or authorized service providers that have a legitimate business need for
the information. We maintain physical, electronic and procedural safeguards designed to protect the nonpublic personal information of our stockholders.